Differential gas lift system



Aug M? l970 c. H. HOLLADAY, JR 3,523,744

DIFFERENTIAL GAS Ll'FT SYSTEM Filed Deo. 2. 1968 3,523,744 Patented Aug. l1, 1970 3,523,744 DIFFERENTIAL GAS LIFT SYSTEM Collis H. Holladay, Jr., Olney, Ill., assignor to Baker Oil Tools, Inc., City of Commerce, Calif., a corporation of California Filed Dec. 2, 1968, Ser. No. 780,475 Int. Cl. F04f 1/12, 1/00, 1/08 US. Cl. 417--115 18 Claims ABSTRACT F THE DlSCLSURE A well bore gas lift system for lifting Well bore liquid through a tubing string to the well bore top. Two differential valves feed gas from the tubing-casing annulus into the tubing string, one valve being arranged to operate at a normal high pressure differential setting and the other valve at a very low pressure differential setting. The high-set valve rst opens and assists the low-set valve to then open, the low-set valve first closes and assist the high-set valve to then close.

The present invention relates to subsurface well bore apparatus, and more particularly to a differential gas lift system used to inject relatively high pressure gaseous fluid into a tubing string disposed in a well bore, for the purpose of elevating the liquid in the tubing string to the surface or top of the well bore.

Under some Well conditions, gas lift equipment used for elevating liquid through the tubing string to the top of the well bore does not operate properly or efficiently. The gas lift valve may open at the desired pressure differential between the gas pressure in the tubing-casing annulus and the pressure in the tubing string, but the gas lift valve does not close upon the arrival and discharge of the slug of liquid at the top of the Well bore. For the gas lift valve to close, the tubing pressure must reduce to a certain level below the tubing-casing annulus pressure to provide a required valve closing differential pressure. The failure of the valve closing differential pressure to be realized may also present itself Where the tubing-casing annulus pressure is reduced excessively, as by low deliverability of gas into the annulus, and by the presence of a small diameter casing in the well bore.

It is desirable for a large port area to be present in the differential valve mechanism, through which the gas under pressure can flow, for eicient ballistic lifting to occur. Such large port area provides a high flow rate of gas. Where such high flow rate is coupled with the presence of wet gas in the tubing-casing annulus, and further with the necessity for lifting the liquid through comparatively a long tubing string, valve closure is prevented after the desired quantity of the liquid has been discharged at the top of the well bore.

By virtue of the present invention, a large gas lift valve port area is provided through which the gas can enter the tubing string for the purpose of creating high flow of gas for ecient lift of the slug of liquid in the tubing string to the top of the well bore. Despite the -presence of such large port areas, and even in the presence of wet lifting gas and a long tubing string, the valve device will still close at the required valve closing differential. This will occur despite the fact that the large rate of gas flow through the tubing string will increase the pressure in the tubing string to the point at which the gas lift valve mechanism would otherwise remain in an undesired open condition.

More specifically, the invention contemplates the provision of a multiplicity of gas lift valves at the gas injecting point in the tubing string, which, for example, may consist of two differential gas lift valves. One of the gas lift valves is set to operate at a normal, comparatively high pressure differential, while the other gas lift valve is set to operate at a very low pressure differential; that is to say, the high-set pressure differential valve will open and will close when the tubing pressure is at a certain value compared to the tubing-casing annulus pressure; whereas, the very low differential pressure will open and will also close when the tubing pressure is at a much higher pressure. The high-set differential gas lift valve will first open to allow gas to flow into the tubing string, such ow of gas elevating the pressure in the tubing string to the point at which the low-set differential gas lift valve will open, so that the gas flowing therethrough will combine with the gas owing through the high-set differential valve and assist the elevation of the slug of liquid in the tubing string to the top of the well bore. When the pressure in the tubing string drops to a certain value, the low-set pressure differential valve will close, but the high-set pressure differential valve will remain open. The closing of the low-set pressure differential valve will reduce the flow of gas into the tubing string and will reduce the pressure therewithin to the point at which the high-set pressure differential valve will also close. Thus, the high-set pressure differential valve assists the low-set pressure differential valve to open; whereas, the low-set pressure differential valve assists the high-set pressure differential valve to close. The two differential valves provide a large combined port area with improved operating characteristics to secure eicient ballistic lift of the slug of liquid in the tubing string, and such improved operating characteristics of the system are of particular advantage in wells where wet gas must be used for effecting lifting of the slug in long tubing strings. It is also effective where the tubing-casing annulus pressure may drop because of low deliverability of gas thereto.

This invention possesses many other advantages, and has other purposes which may be made more clearly apparent from a consideration of a form in which it may be embodied. This form is shown in the drawings accompanying and forming part of the present specification. It will now be described in detail, for the purpose of illustrating the general principles of the invention; but it is to be understood that such detailed description is not to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

Referring to the drawings:

FIG. l is a diagrammatic view of a differential gas lift system embodying applicants invention;

FIG. 2 is a longitudinal section through one of the gas lift valves embodied in the system disclosed in FIG. 1, with the valve in closed position; and

FIG. 3 is a view similar to FIG. 2, with the valve in open position.

The differential gas lift system disclosed in the drawings as illustrative 0f the invention is presented diagrammatically in FIG. 1. An oil well W has a casing string B therein, with fluid from a deep storage well C capable of passing through casing perforations D to the casing interior. A Well packer E may be set in the casing string above the perforations and a tubing string T is disposed in leakproof relation to the packer so that the well fluid can flow upwardly through the tubing string to the top of the well bore, the tubing string extending in sealed relation through a casing head G and into a production line H under the control of a surface valve .T In some instances, the Well packer need not be used, the gas from the storage Well C passing into the casing-tubing annulus K and to the top of the well bore, there being a suitable mechanism (not shown) in the lower portion of the tubing string T to control the lifting of water from the gas zone C upwardly through the tubing string T, this water being removed when it reaches a certain elevation in the tubing string, as described hereinbelow.

As specifically disclosed in the drawings, a plurality of gas lift valves R, S are mounted on the tubing string closely adjacent to the well packer E, these gas lift valves controlling the injection of gas from the casing-tubing annulus K into the tubing string, the gas being supplied from a suitable compressor or supply line through the gas line L into the upper portion of the casing string, there being a suitable valve M for controlling such iiow of gas. The lower gas lift valve S is set to open at a relatively high casing annulus-tubing pressure differential; whereas, the other gas lift valve R is set to open at a substantially lower casing annulus-tubing pressure differential. The differential gas lift valves employed have a large port area through which gas can flow into the tubing string T when each valve is in open condition, the specific valves illustrated in FIGS. 2 and 3 of the drawings being of the type described and claimed in the application of David V. Chenoweth, for Differential Pressure Gas Lift Valve, filed Oct. 3, 1968, Ser. No. 764,738.

As described in the above patent application, each differential gas lift valve includes a fitting suitably secured, as by welding, to the exterior of the tubing string T and having its internal passage 21 communicating with the interior of the tubing string T through a port slot 22. The lower portion 23 of the fitting is internally threaded for threaded attachment of a differential gas lift housing 24 thereto, which has an upwardly facing valve seat 25 adapted to be engaged by a ball check valve element 26 to prevent reverse fiow of uid from the tubing string T into the tubing-casing annulus K, this housing also having a cylindrical valve seat 27 with an area Av adapted to be closed by the upper valve head portion 28 of a piston valve member 29 slidably mounted in the inner bore of the housing below a plurality of side chokes or orifices 30 opening through the wall of the housing below the valve seat 27. Upward movement of the piston valve 29 is limited by engagement of its shoulder 31 with a companion downwardly facing shoulder 32 on the housing, at which time the valve head 28 Will be disposed Within the cylindrical seat 27, leakage of liuid between the head and seat being prevented by a suitable side seal ring 33 mounted in a groove 34 in the head and sealingly engaging the valve seat 27. When the valve head is sealingly engaged with the seat, the head itself has engaged the ball check valve member 26 and elevated it from its companion valve seat 25, so that the fiuid pressure Pp in the tubing string can act in a downward direction over the area Av of the valve head.

The piston valve member 29v is shiftable downwardly to a position in which its valve head 28 is completely removed from the valve seat 27, opening the chokes 30 to the passage of gas from the tubing-casing annulus K through the valve seat 27 and into the tubing string T. Downward movement of the piston valve is limited by engagement of a downwardly facing piston shoulder 35 with a suitable stop ring 36, in the form of a split snap ring, mounted within an internal groove 37 in the lower portion of the valve housing 24. Such downward shifting of the valve head occurs as a result of the combined action of the fluid pressure Pt in the tubing string, acting downwardly over the area AV of the piston valve, and a tension spring 38, the upper end of which is suitably connected to the lower end of the piston valve 29, the lower end of the spring being suitably connected to a spring anchor member 39 welded, or otherwise attached, to the exterior of the tubing string T, the spring being protected by a suitable enclosure 40. When the piston valve member 29 is in its downward or full port opening position, the spring 38 may have very little tension in it. However, when the valve is in its closed position, the spring may have substantial tension.

It is to be noted that the gas pressure Pc in the tubingcasing annulus K acts in an upward direction over the area Ap of the piston valve, which area is much greater than the area A,l of the upper valve head portion 28 of the piston valve. When the valve is closed, the gas pressure is also acting in a downward direction over the annular area AX of the large diameter piston portion 41, which is the area between the cylindrical valve seat 27 and the larger diameter surface 42 of the cylindrical portion of the housing in which the piston slides. When the valve is in the closed condition, the gas pressure can still pass through the choke 30 to the interior of the housing above the piston shoulder having the area Ax and act downwardly on the piston valve 29. The gas pressure acting over this area AX makes the resultant area over which the gas pressure acts, with the valve in the closed condition, the same area A, as the area Av of the seat 27 of the gas lift valve; that is, Ap-AX=AV.

Thus, with the valve in the closed condition (FIG. 2), the tubing pressure P1, is acting downwardly over the area Av, tending to shift the piston valve to open position. The gas pressure in the tubing-casing annulus K is acting upwardly over the area Ap-Ax, or Av, tending to maintain the piston valve 29 in the closed position. The-spring 38 is acting over the piston valve in a downward direction, supplementing the force of the tubing pressure and tending to shift the valve downwardly to open position. When the liquid level in the tubing string has risen sufficiently, so that its downward force on the piston valve supplemented by the spring force exceeds the force of the gas pressure acting upwardly on the piston valve, the piston valve will be shifted downwardly to an open condition and the gas under pressure can then fiow through the opened ports 30 and through the valve seat 27, past the ball check valve element 26 and through the tubing port 22 to the interior of the tubing string T, lifting the slug or column of liquid ahead of it to the top of the well bore. The gas pressure PV within the valve housing 24 on the downstream side of the orifices 30, which will be less than the gas pressure Pc in the tubing-casing annulus K, because 0f the throttling action of the orifices 30, will then be acting in a downward direction on the piston valve 29 over its full area Ap, this force being supplemented by the force of the spring 38 which can then be rather low to maintain the piston valve member in the open condition. However, if the slug of liquid is discharged at the top of the well bore, the fiow of gas through the orifices 30 accelerates, the gas pressure PV on the downstream side of the orifices in acting downwardly on the piston valve 28 decreasing until it and the spring 38 are insufiicient to hold the valve 29 in a downward or valve opening condition, the greater gas pressure in the tubing-casing annulus K acting upwardly over the area Ap of the piston valve and shifting it to the closed condition.

By making the area Ap over which the gas pressure Pv acts, with the valve in the open condition, greater than the area Av over which the tubing pressure Pt acts when the valve is in the closed condition, the area Ac of the orifices or chokes 30 can be made much greater, since the larger piston area Ap compensates for the smaller pressure drop created by the enlarged chokes or orifices 30. Thus, there is still provided a differential valve that will open and close at approximately the same differential pressure.

In the operation of the gas lift valve disclosed in FGS. 2 and 3, let it be assumed that it has been installed in the tubing string T at a location close to and above the well packer E, that the tubing-casing annulus K has been unloaded down to the location of the gas lift valve, and that the liquid level in the tubing string T from the Well formation C has reached a level in the tubing string at which the tubing pressure Pt plus the spring force open the gas lift valve. The gas under pressure can then flow through the orifices 30 and through the gas lift valve into the tubing string T to lift the liquid to the top of the well bore. As the liquid is being discharged, the velocity of gas through the orifices increases, and the pressure P., inside the valve body 24 and on the downstream side of the orifices 30 will decrease to the point at which the gas pressure Pc in the tubing-casing annulus K will shift the valve to a closed condition. Despite the use of larger area chokes or orifices 30, the pressure differential required to close the -valve will be approximately the same as the pressure differential between the gas pressure Pc and the tubing pressure Pt to open the valve, the small spread between the two pressure differentials being due to the fact that the greatly increased area of the chokes or orifices 30 is compensated for by the fact of the arca Ap of the piston valve, over which the gas pressure P.. acts, is substantially larger than the area Av of the valve seat 27.

The gas lift valve will remain closed until the liquid level in the tubing string has again risen to the point at which the tubing pressure Pt plus the spring force can overcome the force of the tubing-casing annulus gas pressure Pc acting over the differential area AV of the piston valve 29 (Ap-AX), when it is in the closed condition, and the foregoing cycle of operation will be repeated.

The gas lift valve specifically `described above has the very desirable characteristic of large orifice ports 30 therethrough, to permit a large flow rate of gas into the tubing string T when the valve is in the open position (FIG. 3), which results in efficient ballistic lift of the liquid slug in the tubing string to the top of the well bore., However, in some well installations, tubing pressure Will1 not drop sufficiently to close the differential valve, inasmuch as the tubing pressure does not reduce to the point at which the differential pressure increases to the Valve closing condition. By virtue of the present invention, the difficulty is solved in that a large port area is provided to allow high gas rates of flow into the tubing string, while assurance is had that each gas lift valve R, S will close at the required valve closing differential pressure.

In place of a single differential gas lift valve with a large port area being presented, such as the single differential valve illustrated in FIGS. 2 and 3, a plurality of differential valves, such as two differential valves R, S, are connected to the tubing string T. Each differential valve will have about one-half the port area, so that the two differential valves, when open at the same time, will provide a combined port area of the desired value. One of the differential gas lift valves, such as the lower gas lift valve S, is set to open and close at a high pressure differential; whereas, the adjacent upper gas lift valve R is set to operate at a low pressure differential. The spring 38 of the upper low-set differential valve R may exert a lesser force tending to open the valve than the spring of the high-set differential gas lift valve S. Accordingly, as the liquid level in the tubing string T rises with both gas lift valves closed, the high-set differential Valve S will open first, and such opening pressure may be at the desired tubing pressure P1, build-up. When the high-set differential valve opens, gas will flow through its ports 30 and into the tubing string to begin elevating the slug of liquid in the tubing string, but, at the same time, also increasing the fluid pressure Pt in the tubing string, causing the annulus-tubing pressure differential to decrease below the setting of the low-set differential gas lift valve R, such low-set differential gas lift valve then opening. As a result, both gas lift Valves R, S are now open and the tubing-casing annulus gas is passing through the combined areas of the ports or orifices 30 of the two valves into the tubing string, for efficiently lifting the slug of fluid in the tubing to the top of the well bore. During discharge of the liquid slug at the top of the well bore, the tubing pressure Pt progressively decreases, and when it reaches a value below the tubing-casing annulus pressure that provides the required differential for closing the lowset differential valve R, such valve will close. The gas can then flow only through the high-set differential gas lift valve, passing through its ports 30 of a lesser area than the combined port areas of both differential gas lift valves, not only reducing the quantity of gas injected into the tubing string T, but also the pressure in the tubing string. When such pressure reduces sufficiently, the highset differential gas lift valve S will close.

The foregoing cycle of operation will be repeated intermittently. Assuming both valves R, S to be closed, the high-set differential gas lift valve S will first open, and such opening will effect opening of the low-set differential valve R. When the tubing pressure Pt has decreased as a result of discharge of the slug of liquid at the top of the well bore, the loW-set differential valve R first closes, and such closing effects a further reduction of the pressure in the tubing string t0 the point at which the high-set differential valve S closes. Thus, the highset differential valve S opens and triggers the low-set differential valve R to open, the low-set differential valve first closing and triggering the high-set differential valve to close.

I claim:

1. In apparatus for lifting fiuid flowing from a subsurface zone into a well bore: a tubing string in the well bore extending to the top of the well bore and into which fluid from the zone can flow; first and second gas lift valves connected to the tubing string for injecting gas from the well bore externally of the tubing string into the tubing string; said first gas lift valve being constructed and arranged to open at a desired normal difference in pressure between the fluid pressure in the well bore externally of the tubing string and the fluid pressure internally of the tubing string; said second gas lift valve being constructed and arranged to open at a pressure differential which is lower than the opening pressure differential of said first gas lift valve.

2. In apparatus as defined in claim 1; said first and second gas lift Valves being connected to the tubing string at substantially the same location in the well bore.

3. In apparatus as defined in claim l; said first and second gas lift valves being connected to the tubing stringr at locations adjacent to each other.

4. In apparatus as defined in claim l; said first gas lift valve being constructed and arranged to close at a desired normal difference in pressure between the fluid pressure in the well lbore externally of the tubing string and the fluid pressure internally of the tubing string; said second gas lift valve being constructed and arranged to close at a pressure differential which is lower than the closing pressure differential of said first gas lift valve.

5. fn apparatus as defined in claim 1; said first gas lift valve 'being constructed and arranged to close at a desired normal difference in pressure, between the fluid pressure in the Well bore externally of the tubing string and the fluid pressure internally of the tubing string; said second gas lift valve being constructed and arranged to close at a pressure differential which is lower than the closing pressure differential of said first gas lift valve; said first and second gas lift valves being connected to the tubing string at substantially the same location in the well bore.

6. In apparatus as defined in claim 1; said first gas lift valve being constructed and arranged to close at a desired normal difference in pressure between the fiuid pressure in the well bore externally of the tubing string and the fiuid pressure internally of the tubing string; said second gas lift valve being constructed and arranged to close at a pressure differential which is lower than the closing pressure differential of said first gas lift valve; said first and second gas lift valves being connected to the tubing string at locations adjacent to each other.

7. In apparatus for lifting fluid flowing from a subsurface zone into a lwell bore: a tubing string in the well bore extending to the top of the well bore and into which fluid from the zone can flow; first and second gas lift valves connected to the tubing string for injecting gas from the well bore externally of the tubing string into the tubing string; each gas lift valve having a passage communicating with the interior of said tubing string and also having a valve seat surrounding said passage, means for conducting a gaseous fluid under pressure from the exterior of said valve to said valve seat for flow therethrough into said passage; said conducting means including one or more orifices in said valve on the upstream side of said seat, a valve member shiftable in said valve between a closed position engaging said seat to prevent the gaseous fluid passing through said one or more orifices from flowing through said seat and an open position disengaged from said seat to permit such flow of the gaseous fluid, said valve member being subject to the pressure of the gaseous fluid externally of the valve to shift said valve member toward its closed position, said valve member also being subject to the pressure of the fluid in the tubing string when the valve member is engaged with said seat tending to shift said valve member toward its open position, and supplemental means exerting a force on said valve member tending to shift said valve member toward open position; said first gas lift valve being constructed and arranged to open at a desired normal difference in pressure between the fluid pressure in the well bore externally of the tubing string and the fluid pressure internally of the tubing string; said second gas lift valve being constructed and arranged to open at a pressure differential which is lower than the opening pressure differential of said rst gas lift valve.

8. In apparatus as defined in claim 7; said first and second gas lift valves being connected to the tubing string at substantially the same location in the well bore.

9. In apparatus as defined in claim 7; said first and second gas lift valves being connected to the tubing string at locations adjacent to each other.

10. In apparatus as defined in claim 7; said first gas lift valve being constructed and arranged to close at a desired normal difference in pressure between the fluid pressure in the well bore externally of the tubing string and the fluid pressure internally of the tubing string; said second gas lift valve being constructed and arranged to close at a pressure differential which is lower than the closing pressure differential of said first gas lift valve.

11. In apparatus as defined in claim 7; said first gas lift valve being constructed and arranged to close at a desired normal difference in pressure between the fluid pressure in the well bore externally of the tubing string and the fluid pressure internally of the tubing string; said second gas lift valve being constructed and arranged to close at a pressure differential which is lower than the closing pressure differential of said first gas lift valve; said first and second gas lift valves being connected to the tubing string at substantially the same location in the well bore.

12. In apparatus as defined in claim 7; said first gas lift valve being constructed and arranged to close at a desired normal difference in pressure between the fluid pressure in the well bore externally of the tubing string and the fluid pressure internally of the tubing string; said second gas lift valve being constructed and arranged to close at a pressure differential which is lower than the closing pressure differential of said first gas lift valve; said first and second gas lift valves being connected to the tubing string at locations adjacent to each other.

13. In apparatus for lifting fluid flowing fromy a subsurface zone into a well bore: a tubing string in the well bore extending to the top of the well bore and into which fluid from the zone can flow; first and second gas lift valves connected to the tubing string for injecting gas from the well bore externally of the tubing string into the tubing string; each gas lift valve having a passage communicating with the interior of said tubing string and also having a valve seat surrounding said passage, means for conducting the gaseous fluid under pressure from the exterior of said valve to said valve seat for flow therethrough into said passage, said conducting means including one or more orifices in said valve on the upstream side of said seat, a valve member shiftable in said valve between a closed position engaging said seat to prevent the gaseous fluid passing through said one or more orifices from flowing through said seat and an open position disengaged from said seat to permit such flow of the gaseous fluid, said valve member having a first surface subject to the pressure of the gaseous fluid externally of the valve tending to shift said valve member towards its closed position, a second surface subject to the pressure of the fluid in the tubing string when the valve member is engaged with said seat tending to shift said valve member toward its open position, and a third surface subject to the pressure of the gaseous fluid in the valve between said valve seat and said one or more orifices tending to urge said valve member in a direction away from said valve seat, the area of said rst surface and said third surface each being greater than the area of said second surface, and supplemental means exertinga force on said valve member tending to shift said valve member toward open position; said first gas lift valve being constructed and arranged to open at a desired normal difference in pressure between the fluid pressure in the well bore externally of the tubing string and the fluid pressure internally of the tubing string; said second gas lift valve being constructed and arranged to open at a pressure differential which is lower than the opening pressure differential of said first gas lift valve.

14. An apparatus as defined in claim 13; said first and second gas lift valves being connected to the tubing string at substantially the same location in the well bore.

15. In apparatus as defined in claim 13; said first and second gas lift valves being connected to the tubing string at locations adjacent to each other.

16. In apparatus as defined in claim 13; said first gas lift valve being constructed and arranged to close at a desired normal difference in pressure between the fluid pressure in the Well bore externally of the tubing string and the fluid pressure internally of the tubing string; said second gas lift valve being constructed and arranged to close at a pressure differential which is lower than the closing pressure differential of said first gas lift valve.

17. In apparatus as defined in claim 13; said first gas lift valve being constructed and arranged to close at a desired normal difference in pressure between the fluid pressure in the well bore externally of the tubing string and the fluid pressure internally of the tubing string; said second gas lift valve being constructed and arranged to close at a pressure differential which is lower than the closing pressure differential of said first gas lift valve; said first and second gas lift valves being connected to the tubing string at substantially the same location in the well bore.

18. In apparatus as defined in claim 13; said first gas lift valve being constructed and arranged to close at a desired normal difference in pressure between the fluid Y pressure in the well bore externally of the tubing string and the fluid pressure internally of the tubing string; said second gas lift valve being constructed and arranged to close at a pressure differential which is lower than the closing pressure differential of said first gas lift valve; said rst and second gas lift valves being connected to the tubing string at locations adjacent to each other.

References Cited UNITED STATES PATENTS 3,225,783 12/1965 Stacha 103-232 X 3,318,258 5/7967 Luigs 103-233 X 3,342,203 9/1967 Abercrombie 137-155 3,372,650 3/1968 Garrett 10'3-233 DONLEY I. STOCKING, Primary Examiner W. I. KRAUSS, Assistant Examiner 

